This invention relates to the cracking of hydrocarbons. In another aspect, this invention relates to a catalytic cracking process which uses a passivation agent and an oxidation promoter simultaneously. Still another aspect of this invention is a catalyst cracking process wherein the afterburning is controlled. Still another aspect of this invention relates to the use of a metals passivation agent in a cracking unit which also uses a catalyst containing a combustion promoter without encountering regenerator afterburning problems. In still another aspect, this invention relates to a cracking catalyst process which uses a passivation agent and an oxidation promoter simultaneously wherein the charge rate of the oxidation promoter is increased an effective amount at about the same time the passivation agent is charged to the reactor at an excessive rate.
It is well known that in the catalytic cracking process for converting gas oil, and the like to gasoline that heavy metals such as nickel and vanadium in the feedstock deposit on the catalyst, imparing its activity for converting heavier hydrocarbons to gasoline while enhancing its activity for converting hydrocarbons to coke and hydrogen, a most undesirable result.
Recently it has been found that the addition of various antimony compounds or other agents to the catalyst can passivate the contaminating metals and restore the catalyst to near its original activity. The passivation compound can be added directly to the catalyst or can be continuously supplied to the cracking unit, for example, by incorporating the agent in the hydrocarbon feed to the unit. The latter method is generally preferred. Examples of suitable antimony passivating agents are disclosed in U.S. Pat. No. 3,711,422 and 4,025,458, which are incorporated by reference herein.
Another well-known group of agents useful in catalytic cracking are the combustion promoters. These include many metals in Groups IB, IIB, IVB, VA, VB, VIB, VIIB, and VIII and compounds thereof. Examples of appropriate agents are disclosed in U.S. Pat. Nos. 3,136,713, 3,364,136, and 4,036,740. These agents, which are generally incorporated into the catalyst before use, promote the combustion of CO in the catalyst regenerator and thereby help prevent or minimize the problem of afterburning which is the combustion of CO in the dilute phase of the regenerator to thereby cause undesirable high temperatures in the upper part of the regenerator vessel, including the cyclones.
Problems have been encountered, however, when a passivation agent and an oxidation promoter are used simultaneously in a catalytic cracker. It has been found that when a passivation agent is used in a cracking unit in which the catalyst contains a combustion promoter the performance of the promoter is impaired and the tendency toward regenerator afterburning increased. This effect is most pronounced when the passivation agent is initially charged to a cracking unit. During this period the passivation agent is charged at a high rate, generally two to 100 times the normal maintenance rate, in order to build up the concentration of passivation agent on the catalyst to an effective level. During the latter part of such a buildup period and for some time thereafter, the activity of the promoter is reduced and difficulty with afterburning is encountered.
Accordingly, it is an object of this invention to provide an improved cracking process using a passivating agent and an oxidation promoter simultaneously.
Another object of this invention is to provide a novel process for controlling and reducing the afterburning in a cracking process caused by a reduction in the oxidation promoter's activity due to the presence of a metal passivation agent while maintaining an essentially constant regenerator air flow rate.
Yet a further object of this invention is to provide a cracking process which uses both a passivation agent and an oxidation promoter effectively by overcoming the problems of using the two agents simultaneously.
Other objects, aspects, and the several advantages of this invention will be apparent to those skilled in the art upon a study of this disclosure and the appended claims.